1. Field of the Disclosure
The present disclosure relates to a controller and a control method for controlling a feed apparatus for moving a movable body.
2. Background of the Disclosure
The feed apparatus generally has a guide unit for guiding movement of the movable body and a drive unit for moving the movable body, and, for example, the guide unit comprises a rolling guide mechanism or a sliding guide mechanism, while the drive unit comprises a ball screw, a nut fixed to the movable body and screwed to the ball screw, and a drive motor for rotating the ball screw about its axis to move the nut and the movable body coupled to the nut.
The controller controlling the feed apparatus is configured to generate a control signal based on a target movement position of the movable body and drive the drive motor under the control signal to cause the drive motor to rotate the ball screw about its axis so as to move the movable body to the target movement position.
Incidentally, as a representative example of a field to which the above-described feed apparatus is applied, the field of machine tools can be given. However, beside this field, the feed apparatus is applied to various fields, and, in recent years, highly accurate positioning control is more and more required. In particular, there is a problem that, if tracking delay occurs when reversing the feeding direction, a so-called “quadrant glitch” occurs in a case where the feed apparatus has two or more feed axes and the feed axes are controlled simultaneously.
In view of such background, conventionally, attention has been given to friction inherent in the feed apparatus as one of the factors causing a tracking error of the movable body and various researches have been made for compensating for a tracking error caused by the friction. According to such conventional researches, it is considered that, in the feed apparatus, a uniform (constant) Coulomb friction occurs before reversing the movable body, while non-linear friction variation occurs in a certain section as a transition period after reversing the movable body and then a uniform Coulomb friction occurs.
The inventors of this application have already suggested a controller disclosed in Proceedings of Joint Technical Meeting on Industrial Instrumentation and Control/Mechatronics Control, IIC-13-026/MEC-13-026 as a controller which effectively corrects a tracking error due to such friction. This controller has a friction compensation unit for compensating for a tracking error due to friction, and the friction compensation unit is configured to calculate a compensation value in accordance with the following Equation 3 (Sinc-Function-Based Friction Compensation Model) and apply a current which has been corrected in accordance with the calculated compensation value to a drive motor, thereby compensating for the tracking error of the movable body.
                              f          ⁢                                          ⁢                      (            x            )                          =                  {                                                                                          -                                          F                      0                                                        ,                                                                              x                  <                  0                                                                                                                                                2                      ⁢                                                                                          ⁢                                              F                        0                                            ⁢                                                                        sin                          ⁢                                                                                                          ⁢                                                      (                                                                                          π                                ⁢                                                                                                      x                                    /                                                                          x                                      s                                                                                                                                                                  -                              π                                                        )                                                                                                                                π                            ⁢                                                                                          x                                /                                                                  x                                  s                                                                                                                                              -                          π                                                                                      -                                          F                      0                                                        ,                                                                              0                  ≦                  x                  <                                      x                    s                                                                                                                                            F                    0                                    ,                                                                              x                  ≧                                      x                    s                                                                                                          [                  Equation          ⁢                                          ⁢          3                ]            
It is noted that, in Equation 3, a position of x=0 is a reversing position and x represents a distance to the movable body from the reversing position, where x is negative (x<0) before reversing and is positive (x>0) after reversing.
In the friction compensation unit, as represented by the above Equation 3, a friction value before the movable body is reversed is estimated to be a constant value (−F0), a friction value in a subsequent certain section including the time of reversing the movable body (0≦x<xs) is estimated by a non-linear sinc function, and a friction value after the certain section (xs≦x) is estimated to be a constant value (F0), and, as described above, the friction compensation unit compensates for the tracking error of the movable body by calculating a friction compensation value in accordance with the friction value estimated by Equation 3 and applying a current which has been corrected in accordance with the calculated friction compensation value to the drive motor.
Thus, according to the controller suggested by the inventors, the accuracy of positioning the movable body can be improved as compared with other conventional controllers.